The present invention relates to a solid state image sensing device suitable for use as broadcasting triple cameras, still cameras, copying machine, facsimile, etc. and a method of making the same device.
As the prior art solid state image sensing device used for broadcasting triple cameras and still cameras, there is a well known structure such that a light reflection preventing film such as a black filter is formed between columns of two-dimensionally arranged photosensitive portions. This light reflection preventing film is effective to prevent light reflected from light shielding films (formed away from the photosensitive portions) from being allowed to be incident again upon the photosensitive portions, thus improving the flare characteristics. The solid state image sensing device provided with the light reflection preventing film as described above is mainly adopted for high performance solid state image sensing device for broadcasting use, for instance.
In the solid state image sensing device as described above, photodiode portions which constitute photosensitive portions and CCD portions are formed on the surface of a semiconductor substrate. Further, a black light reflection preventing film is provided over the CCD portions via a transparent photo-crosslinking smoothing layer hardened by light irradiation, and additionally a lens layer of a semicircular cross-section is formed over the photodiodes via a similar smoothing layer, for improvement of photosensitivity of the photosensitive portions. Further, a protective layer made of the same material as the smoothing layer is formed on the uppermost layer of the device.
Further, in the case of the image sensing devices used for apparatus (e.g., still cameras) which require an excellent color reproducibility, there is known a device in which three primary color (green, red and blue) filters of different layers are formed being arranged in, for example, strip fashion in the column direction so as to correspond to the two dimensionally arranged photodiodes.
There are also known a device of complementary color type which is mainly used for home-use camcorder and a device having a one dimensionally (linearly) arranged photodiodes which is mainly used for copying machines, facsimiles, etc. In the solid state image sensing device as described above, resist printing layers are formed between the two color filter layers, respectively and a protective layer is further formed on the uppermost layer. These layers are all formed of transparent photo-crosslinking layers.
In the solid state image sensing device as described above, the construction is such that bonding pads for providing electrodes are formed spaced apart from the photodiode portions and the CCD portions; and the smoothing layers, resist printing layers and protective layer are all removed over the bonding pads in order to provide the electrodes.
In manufacturing the prior art solid state image sensing device as described above, it is important to make smooth the surfaces of the respective layers, and therefore the these layers are formed of a transparent smoothing layer of photo-crosslinkage type, respectively, as already described. To form the smoothing layer, a chemical such as acrylic polymer with photosensitive chemical, for example, "FVR" (Trademark of FUJI YAKUHIN) is applied all over the surface and then selectively exposed to light, and then developed by methyl ethyl ketone liquid, for instance.
Further, in the method of manufacturing the prior art solid state image sensing device, it has been necessary to remove various film materials formed over the bonding pads in order to secure the electrical connection to the solid state image sensing devices, in the process for forming color filters on the surface of the semiconductor substrate. For facilitation of the removal of the film forming materials, it has been necessary to use the material of photo-crosslinked type for the transparent resin layers such as the smoothing layers, resist printing layers, and protective layer, except the light reflection preventing film, the color filters, and the lens layer.
However, in the case of the present transparent photo-crosslinking resin material such as the above-mentioned "FVR" of FUJI YAKUHIN, a perfect cross linkage rate is not obtained by light exposure, and additionally there exists a problem in that the transparent resin layer tends to shrink due to thermal hysteresis after patterning process.
As described above, since the dimensions of the light reflection preventing film, the color filters, and the lenses are subjected to variation due to shrinkages of the smoothing layers, the photoresist printing layers, and the protective layer all enclosing these film, filters and lenses, it has been so far necessary to design the pattern under due consideration of the shrinkage after light exposure. In this case, however, there still exists a problem in that the previously anticipated shrinkage rate fluctuates due to the variation of the thermal process, manufacturing control conditions or the dispersion between the material manufacturing lots. In the case of the solid state image sensing device, when the relative positional relationship among the color filters, the light reflection preventing film, and the lens layer changes being offset from the designed values, the quality of the image is markedly deteriorated. In the case of 1/3 inch size CCD device having 400 thousand pixels, for instance, although the pitch of the pixels is on the order of 10 .mu.m, when the relative positional offset is on the order of several micrometers, a serious problem arises in that defective bright or dark straight lines 101 are observed in the vertical direction on a video picture 100, as shown in FIG. 5, thus resulting in defective products.